Tolkien - min vän Ronald och hans världar (Swedish: Tolkien - My Friend Ronald and his Worlds) is a Swedish-language book by Arne Zettersten which investigates the sources of J.R.R. Tolkien's legendarium. The book is noteworthy for the reminiscences of Tolkien by Zettersten.

From the back cover

Most people know that J.R.R. Tolkien has been voted for being the author of the 20th century and is considered to be the creator of the modern fantasy literature. It is less known that a Swedish linguist, professor Arne Zettersten, worked with Tolkien in a project of publishing medieval texts during the 1960s and 1970s in Oxford.

The book on "my friend Ronald" provides a fresh reading of the greatly visualized fantasy fiction of Tolkien, in relation to his scientific works on linguistics and his unique life-experiences. Arne Zettersten recollects his memories of the linguistic equilibrist Tolkien, who spoke, wrote and reconstructed living, dead and invented languages.

The book centers around the communicative ability of Tolkien, as well as the relationship between his informal, scientific, and fictive worlds.